Various blood analysis techniques require clear plasma samples free of red cells. Separation of plasma from red cells can be accomplished by various methods based on the fact that the red cells are of a higher specific gravity than the plasma. For example, if a blood sample can be allowed to stand for two or more days, the red blood cells will settle to the bottom by gravity. A faster technique is centrifugation using an ordinary laboratory centrifuge. In routine laboratory analysis, a centrifugation step does not delay the work flow. However, centrifugation does take some time (20 minutes or so) and may be unacceptable in an emergency situation, for example in an operating room. Even in non-emergency situations such as in a doctor's office, it may be desirable for the doctor himself or an assistant to be able to quickly obtain a clear plasma sample without having to send the blood sample to a laboratory.